As a constituent material of a connector, a terminal, a relay, a spring, a switch, and the like which are used in electrical components, electronic components, vehicle components, communication apparatuses, electronic and electric apparatuses, and the like, a copper alloy sheet having high conductivity and high strength has been used. However, along with recent reduction in size and weight, and higher performance of apparatuses, a very strict characteristics improvement has been also required for the constituent material that is used for the apparatuses. For example, a very thin sheet is used for a spring contact portion of a connector. However, it is required for a high-strength copper alloy constituting the very thin sheet to have high strength, and a high degree of balance between elongation and strength so as to realize small thickness. Furthermore, it is also required for the copper alloy sheet to be excellent in productivity and economic efficiency, and to have no problem in conductivity, corrosion resistance (stress corrosion cracking resistance, dezincification corrosion resistance, migration resistance), stress relaxation characteristics, solderability, and the like.
In addition, in the constituent material of a connector, a terminal, a relay, a spring, a switch, and the like which are used in electrical components, electronic components, vehicle components, communication apparatuses, electronic and electric apparatuses, and the like, a component and a portion in which relatively high strength or relatively high conductivity are necessary are present due to a demand for small thickness on the assumption that elongation and bending workability are excellent. However, the strength and the conductivity are characteristics that conflict with each other, and thus when strength is improved, conductivity generally decreases. Among these, there is present a component which is a high-strength material, and for which relatively higher conductivity (32% IACS or more, for example, approximately 36% IACS) is required at tensile strength, for example, of 500 N/mm2 or more. In addition, there is also present a component for which further excellent stress relaxation characteristics and heat resistance are required, for example, at a site at which a use environment temperature is high such as a site close to an engine room of a vehicle.
As a high-conductivity and high-strength copper alloy, generally, beryllium copper, phosphor bronze, nickel silver, brass, and Sn-added brass are known in the related art, but these general high-strength copper alloys have the following problem, and thus these alloys may not meet the above-described demand.
Beryllium copper has the highest strength among copper alloys, but beryllium is very harmful to the human body (particularly, in a melted state, it is very dangerous even in an infinitesimal amount of beryllium vapor). Therefore, waste disposal (particularly, incineration disposal) of members formed from beryllium copper or products including the members is difficult, and an initial cost necessary for melting facilities used for production is very high. Accordingly, there is a problem of economic efficiency including a production cost together with a solution treatment at the final production stage to obtain predetermined characteristics.
Phosphor bronze and nickel silver are poor in hot workability, and production thereof by hot rolling is difficult. Therefore, phosphor bronze and nickel silver are generally produced by horizontal type continuous casting. Accordingly, productivity is poor, energy cost is high, and yield is also poor. In addition, expensive Sn and Ni are contained in phosphor bronze for springs or nickel silver for springs, which are representative high-strength kinds, in a large amount, and thus conductivity is poor, and economic efficiency is also problematic.
Brass, and brass to which only Sn is added are inexpensive. However, these do not have satisfactory strength, and are poor in stress relaxation characteristics and conductivity. In addition, there is a problem of corrosion resistance (stress corrosion and dezincification corrosion), and thus these are not suitable for a constituent member of products for realizing reduction in size and higher performance as described above.
Accordingly, such a general high-conductivity and high-strength copper alloy is not satisfactory as a constituent material of components of various kinds of apparatuses in which size and weight tend to be reduced, and performance tends to increase as described above, and development of a new high-conductivity and high-strength copper alloy has been strongly demanded.
As an alloy for satisfying the demand for the high-conductivity and high strength as described above, for example, a Cu—Zn—Sn alloy as disclosed in Patent Document 1 is known. However, even in the alloy related to Patent Document 1, conductivity and strength are not sufficient.